Process for the production of potassium carbamate



' with CO2 etc.

Patented May 28, 1935 STATES PROCESS FOR THE PRODUCTION OF 1 POTASSIUM CARBAMATE Carl Theodor Thorssell and August Kristensson,

Cassel, Germany. r

No Drawing. Application October 24, 1928, Serial No. 314,842. In Germany November 18,1927

.5 clams, (organ-112) J j If'KCOzNHz is mixed with a little water and -;.It is well known thatittis' not possible. to prepare potassium carbonate industrially according to, the ,Solvay process; that is to say by introducing ammonia and carbon dioxide into a solution of potassium chloride. Owing to thecomparatively high solubility of the resulting "KHCOs in comparison. with NH4HCO3, a state of equilibrium occurs even when there. is a small amount of NHiCl and a great deal of KCI in the solution. A separation of these two salts is too complicatedeven if at all possibleto assure a profitable manufacture. The behavior of NH3CO2 and H20 has been dealt with hereabove. Reference is also made to Arbeiten von Terres Zeitschrift fiir Elektrochemie 1921, page 177 concerning these systems. In order to carry out the process, CO2 is introduced in such a strong NH3 NH4CO2NH2 but not (NH4)2CO3 01 NH4H CO3 iS formed. The salt is separated 'by cooling and filtered off. In order to maintain the NHs concentration required for the formation of NH4CO2NH2, NH3 is introduced and then treated Only NH4C02NH2 can be formed in the absence of H20, that is to say in liquid NH3; H2O is required for (NH4)2CO3 as well as for NH4HCO3.

The invention relates to the obtaining of po-' tassium carbonate by means of potassium car bamate.

When CO2 and NH3 areoombined in the form of gases or in solution, it is well known that a mixture of ammonium carbamate and ammonium carbonate is formed. The presence of a great deal of water in the gases or a dilute solution favours the formation of the carbonate, whereas vice versa carbamate is obtained from carbonate by a strong K2003 solution etc.

Moreover ammonium carbamate and ammonium chlorideare very readily soluble in liquid ammonia which is anhydrous or contains very little water, whereas potassium chloride and still more, potassium carbamate are diflicultly soluble therein.

According to theinvention a solid potassium salt, for instance KCl reacts with ammonium carbamate, the mixture being stirred thoroughly in liquid NHs which is anhydrous or contains very little water, so that solid potassium carbamate KCOzNHz, is precipitated, whereas NHQCI, NH4CO2NH2 together with very small quantities of KCOzNHz remain in the solution.

solution that V hartshorn:

heated, NH; or NHs and CO2 .escape, and KHCOa or K2603 or a mixture of these two salts remain behind. This reaction takes placeeven at a comparatively low temperature (below 5 -In carrying out the process, ammonium,.car bamate can be prepared by introducing 002 into an aqueous NH3 solution, whereupon. the 10- solution is cooled and the precipitated salt separated in the pressure filter. The solution is again saturated with NH3 and CO2 introduced afresh.

The ammonium carbamate is then mixed by 15 stirring with solid KCl in liquid NHz.

Instead of ammonium carbamate prepared in this way, for instance salt of hartshorn, prepared from NI-Iz and CO2 by methods ordinarily employed, can be used or CO2 introduced di- 20 rectly into the liquid NHa. When (NH4)2C03 is subjected to a strong dehydrating agent such as liquid ammonia it is immediately converted into carbamate:

Ammonium carbamate is immediately formed by dehydration from the ammonium carbonate or ammonium bicarbonate contained in salt of Ammonium chloride carbamate is also formed when introducing CO2 in dehydrated NH3. The formation into potassium carbamate always takes place by the reaction of potassium chloride with ammonium carbamate.

' The reaction takes place independent of temperature and pressure, so that it is possible i to work at atmospheric pressure and a correspondingly low temperature in which case the NH; is liquid, or at an increased temperature 45 and corresponding pressure.

The precipitate after reaction is completed, and consisting of potassium carbamate and any excess of ammonium carbamate, is sepa rated from the liquid and washed with liquid 50 NH3. The washing liquor is used for fresh mixtures, in order to carry out the process in a circuit.

The separated and washed potassium carbamate is stirred with a little water and heated, 55-

in which case NH3 or NH3 and CO2 escape according to the height of the temperature and are returned to the working process.

The resulting KHCOa or KzCOs represents the final product.

The separated liquid is a solution of NH4C1 with -small quantities of KCOzNI-I 'in liquid NHs.

The NH: is separated from the solution in such'a way that it is obtained again as liquid NHs, which can be done either by ordinary distillation at suitable pressure orby a diminished pressure and re-compression in conjunction with cooling.

The residue which remains after the ammonia is distilled 01f is heated, in which case the small amounts of KCOzNHz contained'therein, react again with NH4C1 to form KCl and NH4CO2NH2.

Upon continued heating the NH4CO2NH2 decomposes into CO2 and NH3, which may thereupon be returned to the manufacturing process. mnco2NH2=2NH3+coz The residue finallyobtained consists of NH4C1 and small amounts of KCl. It is stirredwith water and treated by known methods in the separating apparatus with milk of lime, for the purpose of recovering the NH3 which returns to the manufacturing process.

The new process gives surprising yields: it

is possible to produce up to approximately 100% potash calculated on the potassium salt used.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed we declare that what we claim is:

1. The process of producing potassium carbamate which comprises acting on potassium chloride, dissolved in a substantially anhydrous solvent comprising liquid ammonia, with carbon dioxide.

2. The process of producing potassium carbamate which comprises acting with carbon dioxide on a mixture of potassium chloride with liquid ammonia.

3. The process of producing potassium carbamate which comprises reacting potassium chloride, substantially anhydrous liquid ammonia, and carbon dioxide.

4. The process of producing potassium carbamate which comprises reacting solid potassium chloride, substantially anhydrous liquid ammonia, and carbon dioxide.

5. The process of producing potassium carbamate, which comprises acting with ammonium carbamate on a potassium salt in anhydrous liquid ammonia.

' CARL THEODOR THORSSELL. AUGUST KRISTENSSON. 

